Cathode ray tube for reproducing color television images



March 4, 1958 JONKER ET AL 2,825,845

CATHODE RAY TUBE FOR REPRODUCING COLOR TELEVISION IMAGES Filed April 1,1955 2 Shets-Sheet 1 SOURCE OF sleuAL SOURCE OF SIGNALS OF BANDWIDTH A SN RR I wm TKO 6 NNN H 9 mm A m A H w & T J v m w W D N A B Y F B o A wAA H T W F w N M. WF 80 3 6 March 1958 J. L. H. JONKER ET AL 2,825,345

CATHODE RAY TUBE FOR REPRODUCING COLOR TELEVISION IMAGES Filed April 1,1955 2 SheetsSheet 2 INVENTOR JOHAN LODEWIJK HENDRIX JONKER 55.5 JANCAREL FRANCKEN BY fl fiW AGENT luminesce in diflerent colors. stances orphosphors are arranged in a predetermined 2,825,845 CATHODE RAY TUBE FORREPRODUCING COLOR TELEVISION IMAGES Johan Lodewijk Hendrik .lonker andJan Carel Francken,

Eindhoven, Netherlands, assignors, by mesne assignments, to NorthAmerican Philips Company, Inc., New

York, N. Y., a corporation of Delaware Application April 1, 1955, SerialNo. 498,676

Claims priority, application Netherlands April 3, 1954 16 Claims. (Cl.315-13) The invention relates to cathode-ray tubes and systems forreproducing color television images and, in particular, to cathode-raytubes of the multi-gun type.

One popular cathode-ray tube of the foregoing type comprises threeelectron guns by means of which three concentrated electron beams can bedirected to an image screen containing three luminescent substanceswhich The luminescent submanner, and during operation of the tube areeach excited by a beam of only one electron gun. An input signal issupplied to the control grid of each electron gun, .which comprises atleast a cathode, a control grid, and

an anode constituting a first lens, and a second concentrating orfocussing electron lens. It has been found that it is not necessary forthe three guns to have applied thereto input signals of the samebandwidth, since in order to obtain a satisfactory image it issufiicient for a signal having larger bandwidth to be supplied to onlyone of the guns, which gun then determines the definition of the image.

In most systems in present use, three primary colorsred, green andblueare used, and

for visual observation it has been found to be preferable for thedefinition to be determined by means of the green image. This is easy tounderstand since the human eye has the highest resolving power in thegreen part of the spectrum. However, if desired, the definition mightjust as conveniently be determined by one of the other colors. Althoughnot described, it is obvious that what has been mentioned hereinbeforewith respect to the bandwidth also applies if use is made of only two orof more than three electron guns and of a corresponding number ofprimary colors.

The use of ditierent bandwidths was discovered in an efifort to producea composite color television signal which would not occupy an excessivetotal bandwidth, and which, preferably, would not be larger than thesignal used for black-and-white television. However, the insight gainedas a result of these efforts has so far not influenced the constructionof cathode-ray tubes for use in color television. Normal tubescontaining three identical guns are still used, each gun of whichconsequently produces picture elements of identical size on the imagescreen.

In accordance with the invention, a new construction of the electrodesystem of such cathode-ray tubes is provided to utilize the colortelevision signal and its special bandwidth properties. Thus, thecathode-ray tube according to the invention, comprising an image screenand at least two electron guns, each of which comprises at least acathode, a control-grid, an anode and a second concentrating electronlens, is characterized by a gun structure in which the gun to which thesignal having the largest bandwidth is supplied exhibits a ratio betweenthe relative spacing of the second electron lens and the image screenand the relative spacing of the second lens and the cross-over pointwhich is less than the same ratio in the other electron guns. In itssimplest embodiment,

the second electron lens of the gun to which the largest bandwidthsignal is applied is closer to the image screen than are the secondelectron lenses of the other-guns.

2,825,845 Patented Mar. 4, 1958 ice The term relative spacing of theelectron lens and theimage screen and the term relative spacing of theelectron lens and the cross-over as used herein are to be understood tomeans the distance between the image screen or the cross-over,respectively, and the infinitely thin lens which would have the sameeffect as the said second electron lens. As is well-known, thecross-over" is the constriction of the beam produced in the proximity ofthe control grid, which usually is a diaphragm having a small aperture.

The invention is based upon the fact that the size of the pictureelements on the image screen decreases with a decrease in the ratiobetween the relative spacing of the second electron lens and the imagescreen and the relative spacing of the lens and the beam node orcross-over. Consequently, the gun to which the signal having the largestbandwidth is supplied in a tube in accordance with the invention andthus having the smallest ratio, will produce the smallest pictureelements on the image screen. As indicated hereinbefore, thecolorproducing-component of the screen excited by this gun preferablyproduces a green image. The size of these picture elements andconsequently the absolute values of the two spacings are made such thatthe image has the required definition. With respect to the other guns,one distance or both distances are made difierent with the result thatcertain structural advantages are obtained, as will be set out morefully hereinafter.

In one embodiment, the distances by which the second electron lenses andthe image screen are spaced apart can be made equal ,for all the guns,so that the distance by which the electron lens and the cross-over arespaced apart is smaller for the guns to which the signals having thesmaller bandwidth are supplied than for the gun having the signal oflarger bandwidth supplied to it. Thus, the length of these guns will bereduced with a resultant considerable saving in material, while morespace will become available in the cathode-ray tube.

As an alternative, the second electron lenses of the various guns may bearranged so as to be spaced away from the image screen by variousdistances. This results in a particular structural advantage. Whetherthe electron lenses operate electrostatically or electromagnetically,they substantially always comprise components the diameter of whichexceeds that of their anodes. Since the distance by which they arespaced away from the image screen is different, the axes of the electronguns can, it the differences are properly chosen, be arranged in closerproximity to each other than if the electron lenses were equidistantfrom the image screen and the broad parts of the lenses were arrangedside by side. Consequently, in this embodiment of a cathode-ray tube inaccordance with the invention, the projections of the components of theelectron lenses of the various guns onto a plane at right angles to thetube axis will partially overlap. It will be obvious that due to thisarrangement, a considerable saving in space is obtained, and the neck ofthe tube in which the guns are arranged can be made narrower.

In the last-mentioned construction comprising staggered electron lenses,the object distance and consequently the length of the gun can be variedsubject to the condition that in the gun to which the signal having thelargest bandwidth is supplied, the ratio between the image distance andthe object distance is less than the corresponding ratio of the otherguns.

A very simple construction of a tube containing three guns is obtainedif the axes of the guns are parallel and the second electron lens of thecentral gun is nearer the image screen. Thus, the lengths of the twoouter guns may be made equal, and the central gun maybe made such thatthe cathodes of they three guns are equidistant from the image screen.However, as an alternative, the lengths of the three guns might be madeequal, since in {this case due to the smaller image distance of the lens,of the central gun, :the requirement is fulfilled that this gun hasthe. smallest-magnification. For mass production, it may be advantageousto manufacture only one type of :edges of aright equilateraluprism. Incertain cases, the axes of the guns will preferably be arranged at anangle toeach other such that the electron beams meet in-a point at theimage screen. In .this event, no additional fields are required toconverge the initially-parallel electron .heams.

The invention will now be described more fully with reference to theaccompanying drawing, in which:

Fig. 1 shows diagrammatically the construction of one form ofcathode-raytube according to the inventioncomprising threeelectron guns,the axes of which are parallel .and lie in .one plane;

Fig. 2. shows the neck of another form of cathode-ray tube in accordancewith the invention comprising three electron guns arranged at an angleto each other such ,that their axes meet in a point at the image screen;

Fig. v3 shows the neck ofstill another form of cathoderay tube inaccordance with the invention comprising ethreeelectron guns, theaxes ofwhich form the edges of a right equilateral prism;

.Fig. 4 is a side view .of a tube shown in Fig. "3;

'Fig. 5 shows the neck of another form of cathoderay tube in accordancewith the invention comprising three electron guns the axes of which areparallel andlie ,in one plane, the lengths of the electron guns varyingfrom one gun ,to another.

Referring to Fig. 31, the cathode-ray tube shown consists of ;acylindrical neck' portion 1 and a mating conical part 2 closed off by atransparent window 3. This window supports an electron-receiving,luminescent or fluorescent screen 4, ,In the-neckl of .theatube, threeelectron guns are arranged, in which .the two outer electron guns areidentical. Therefore only one of these guns will be provided withreference numerals. These two guns comprise a cathode 5,.a diaphragm 6acting as a control-grid, an'accelerating orfirstanode 7, another-anode8, .an additional electrode 59 and a final electrode '10. Due to thecooperation .of .the electrodes 5, .6 and .7, which serve as animmersion .or first lens, a cross-over is produced approximately in theaperture of passage of the electrode 6. This crossover, whichconstitutes an optical object, is projected to form an image .on theluminescent screen 4 by means of the second electron lens consisting ofthe electrodes 8, 9 and :10. The electrodes 8, 9 and 10 constitute aso-called unipotential lens, since the electrodes Sand 10 are directlyinterconnected electrically and are thus at the same potential. Theelectrode 9 has a potential applied to it which is lower thanthepotentia-l applied to the electrodes 3 and It). The central electrongun comprises a cathode 14,2. control electrode 15, an accelerating orfirst anode 16, which constitute the immersion lens, .and another anode17, an additional electrode 18 and a final electrode 19. As may be seenfrom the drawing, the unipotential lens constituted by the electrodes17, 18 and 1 9 is arranged nearer the image screen 5%. Consequently, forthis lens, the ratio between the distan in h chis s a e qm h ho c h imascr en 4 a d th istance b wh it i a d t ots th crossover producedapproximately in the aperture of the di ph m .1 s e than he r ondin ti ft lenses of the two remaining electron guns. Thus, the cenneck of thekind 4 tral gun is the gun to which during operation the signals havingthe largest bandwidth are supplied. This is illustrated in Fig. 1 byshowing three signal sources 61, 62 and 63 coupled each to the controlelectrode of one of the three guns. The sources 61 and 62, which arecoupled to the outer two guns, produce color signals of smallerbandwidth A for driving the outer two guns. The third source 63, whichproduces a color signal of larger bandwidth A-l-AA, is coupled to thecenter gun whose ratio of second lens to screen distance and second lensto crossover distance is smaller than the corresponding ratio for theouter'two guns. The three electron beams are deflected with theaid ofdeflector coils 20 and 21 and of two additional coils ensuring thedeflection in the plane of thedr-awing (not shown). Between the electronguns and the ,deflector .coils a field is produced such that-theelectron beams meet in a point 12 .of the image screen 4. 'For'thesakeof clearness, this field which is not important foran'u'nderstanding of the invention is not shown. "However, manyconstructions of electrode systems which operate electromagneticallyand/or electrostaticallyhave been described for bringing together thethree electron beams. As will be seen from the drawing,

the two outer guns are considerably'shorter than the central electrongun. Compared with a tube of known construction, it should .be notedthat the length of the centralelectron gun is the same as the gunsproposed for 'these known tubes. However, the outer guns areconsiderably shorter than the corresponding guns of these known .tubes.

In Fig. 2 la modification is shown in which a neck 22 of a tube containsthree electron guns arranged at an angle to each other such that theiraxes meet in a point of the image screen (not shown). Only the anodesand the ,unipotential second lenses of these guns are shown. As will beseen from the drawing, the three lenses of the guns comprise theadditional electrodes 23, 24 and 25, the widths of which considerablyexceed that of the anodes 26, 27 and 28. Since the lens of the centralgun is arranged nearer the image screen, the outer electron guns may bearranged such that the projections of the electrodes 23, 24 and 25 on toa plane at right angles to the tubes axis 2929 overlap each other. Thisresults in a considerable saving in space, since otherwise the width ofthe neck should be equal to the sum of the diameters of the electrodes23, 24 and 25. In this construction, the electron lenses of the twoouter guns are equidistant from the image screen. However, this is notnecessary and may even be impossible, as will be set out with referenceto Fig. 3.

Fig. 3 shows a further modification comprising three electron guns theaxes of which constitute the edges of a right equilateral prism. In thiscase also, the electron .beams are deflected, similarly to those in theembodiment shown in Fig. 1, 'bymeans of a special field so that theymeet ina point of the collecting screen. In this embodiment, theelectron guns shown diagrammatically by rectangles 30, 31 and 32 areaccommodated in separate tubes 33, 34 and 35. The second electron lensesoperate electromagneticallyand consist of'coils 36, 37 and 38. Theelectron gun 3t) and the coil 36 constitute the system to which thesignal having the largest bandwidth is supplied. As may be seen moreclearly from the side elevation shown in Fig. 4, the axes of theelectron guns form the edges of a right equilateral prism and arearranged in closer proximity to each other than the sum of the radii ofthe circumferences of the coils, which is possible .by means of the factthat the coils are staggered in the direction of their length. In Fig.4, which is a projection on to :a plane at right angles to the tubeaxis, the coils therefore partially overlap. Such an arrangement canalso be used if use is made of electrostatic focussing by means ofwidened cylinders, as is shown in Fig. 2. In Fig. 3, the image screen 4(not shown) is to the left of the figure.

Fig. 5 shows the neck of a further cathode-ray tube in accordance withthe invention comprising three electron guns the lenses of which are ofdifferent construction. The axes of the guns are parallel and lie in oneplane and the lengths of the guns are difierent similarly to theembodiment shown in Fig. 1. The second electron lenses of the outer gunsconsist of electrodes 39, 40 and 41, and 42, 43 and 44, respectively.The second electron lens of the central gun comprises electrodes 45, 46and 47. As will be seen, the width of the electrode 46 exceeds that ofthe anode 45 of the central gun. This results in a better lens. However,since the lenses are arranged so as to be staggered, the axes of theguns may be nearer each other than the sum of the radii of theelectrodes 41 and 46 or 44 and 46 respectively. In this embodiment,additional deflector electrodes 48 and 49 and 50 and 51, respectively,for the outer guns are arranged at the level of the second electron lensof the central gun. With the aid of these sets of deflector electrodes,the two outer electron beams can be converged to the point at which thecentral electron beam strikes the image screen. By the use of theinvention, a very compact construction of the electrode system isobtained, as may be seen from the drawing.

Although the figures only show electron guns comprising an acceleratinganode, this does not mean that this acceleration anode forms anessential part of a tube in accordance with the invention. Use may bemade without further expedients of a so-called triode gun, or a greaternumber of electrodes may, for example, be arranged between the anode andthe cathode. When in describing the invention second electron lenseshave been referred to, only those lenses are meant which are producedbetween the anode and the deflecting field, but not the electron lensproduced between the anode and the accelerating anode.

The description of one specific embodiment similar to that shown in Fig.1 will illustrate the invention. In that embodiment the crossover wasformed approximately at the aperture in the control grids 6 and 15. Thethin lens constituted by electrodes 8, 9 and 10 of the outer guns wasspaced about 60 mms. from the crossover, and about 497 mms. from thescreen 4. Therefore, the ratio was 60 The thin lens constituted byelectrodes 17, 18 and 19 was spaced about 87 mms. from the crossover,and about 470 mms. from the screen. Thus, its ratio of image to objectdistance was which, of course, is smaller than the ratios for the outerWhile we have described our invention in connection with specificembodiments and applications, other modifications thereof will bereadily apparent to those skilled in this art without departing from thespirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A system for reproducing color television images comprising acathode-ray tube, said tube including an electron-receiving screen and aplurality of electron guns, each of said guns including a cathode, acontrol grid and an anode and producing an electron beam having acrossover point, and a plurality of second electron lenses eachassociated with one of said electron guns, the second lens associatedwith one of said guns being positioned so that said one gun exhibits asmaller ratio of lens to screen distance and lens to crossover distancethan that exhibited by the other guns, a source of color signalsincluding at least two separate signals of which one has a largerbandwidth than the other, and means for applying the signal of largerbandwidth to said one gun.

2. A system for reproducing color television images comprising acathode-ray tube, said tube including an electron-receiving screen and aplurality of electron guns, each of said guns including a cathode, acontrol grid and an anode and producing an electron beam having acrossover point, and a plurality of second electron lenses eachassociated with one of said electron guns, the second lens associatedwith one of said guns being closer to the electron-receiving screen thanthe second lenses of the other guns so that said one gun exhibits asmaller ratio of lens to screen distance and lens to crossover distancethan that exhibited by the other guns, a source of color signalsincluding at least two separate signals of which one has a largerbandwidth than the other, and means for applying the signal of largerbandwith to said one gun.

3. A system as set forth in claim 2 wherein the distance between thecrossover and the electron-receiving screen is the same for all theguns.

4. A system as set forth in claim 1 wherein the second electron lensesfor all the guns are spaced the same distance from theelectron-receiving screen.

5. A system as set forth in claim 1 wherein the second electron lensesare unipotential lenses.

6. A system as set forth in claim 1 wherein the second electron lenseseach contain one electrode whose diameter is greater than another of itselectrodes, said one electrode having a diameter at which a projectionthereof on to a plane at right angles to the tube axis will producepartially overlapped images.

7. A system as set forth in claim 1 wherein three guns are providedhaving parallel axes and all lying in the same plane, the second lens ofthe central gun being closer to the electron receiving screen than thesecond lenses of the outer guns, the latter two guns being spaced thesame distance from the image screen.

8. A system for reproducing color television images comprising acathode-ray tube, said tube including a fluorescent screen containing aplurality of color-producing-components and a plurality ofi electronguns each producing an electron beam adapted to cooperate with one ofsaid color-producing-components of said fluorescent screen, each of saidguns including a first immersion lens producing a crossover point ofsaid electron beam and a second electron lens adapted to project saidcrossover point onto said fluorescent screen, the ratio of the spacingsbetween said second lens and said screen and said second lens and saidcrossover point for one of said guns being smaller than thecorresponding ratio for the other guns, a source of color signalsincluding a signal of larger bandwidth and another signal of smallerbandwidth, and means coupling said signal of larger bandwidth to saidone gun and said signal of smaller bandwidth to another of said guns.

9. A system as set forth in claim 8 wherein said second lens is aunipotential lens, and the color-producingcomponent of said screencooperating with said one gun produces green.

10. A cathode-ray tube for reproducing color television imagescomprising an image screen having difierent, color-producing,electron-responsive areas, at least two electron guns each including anelectron lens for producing two electron beams directed at the screen,the lenses of the two guns having difierent ratios of image-to objectspacings with respect to the whole of the screen, said guns producingdifferently-sized picture elements over said screen, and means forcoupling to said guns color signals possessing different bandwidthcharacteristics.

References Cited in the file of this patent UNITED STATES PATENTS2,459,790 Busignies Jan. 25, 1949 2,549,072 Epstein Apr. 17, 19512,570,858 Rajchman Oct. 9, 1951 2,728,025 Weimer Dec. 20, 1955 2,728,872Smith Dec. 27, 1955 CERTIFICATE OF CORRECTION Patent N06 2,825,845

March 4, 1958 Johan Lodewijk Hendrik Jonker et all,

It is hereby certified that error appears in the printed of the abovenumbered patent specification requiring correction and that the saidLetters Patent should read as corrected below Column 2, line 4, for"means" read mean column 6 line 35, for "image" read electron-receivingSigned and sealed this 20th day of May 1958o (SEAL) Attest:

KARL H, AXLINE Commissioner of Patents v t'\. H

UNITED STATES PATENT OFFICE CERTIFICATE OF (IQRRECTION Patent No,2,825,845

March 4 1.958

Johan Lodewijk Hendrik Jonker et al.,

It is hereby certified that error appears in the printed specifica ionof the above numbered patent requiring correction and that the said Leers Patent should read as corrected below Column 2, line 4, for "means"read mean column 6, "image" read electron-receiving 1111a 35 for Signedand sealed this 20th day of May 1958o {(SEAL) Attest:

KARL Ha AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

